Incremental printing of symbolic information – Marking devices
Reexamination Certificate
1999-01-14
2002-07-16
Yockey, David F. (Department: 2861)
Incremental printing of symbolic information
Marking devices
C347S008000, C347S225000, C400S056000, C400S059000
Reexamination Certificate
active
06421073
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to printers, and more particularly it relates to a device for setting the operating distance or spacing between the printing head and the recording carrier (e.g., paper).
2. Discussion of the Related Art
During initialization of matrix and ink drop (e.g., ink jet) printers, for example, and/or upon insertion of a new recording carrier/substrate (e.g., paper), the printer generally positions or repositions the printing head to within a predetermined distance from the recording carrier or substrate. In order to provide accurate and optimum printing operation, it is important that this predetermined distance fall within a predefined tolerance limit for the specific printer. Should the paper thickness change, for example due to the use of single-ply paper of different thicknesses or the use of multi-ply paper or multiple sheets, the position of the printing head relative to the printing abutment must be reset in order to ensure optimum printing quality and (in the case of matrix printers) a long printing head life.
A distance setting device (i.e., a device for adjusting the position of the print head to account for the thickness of the recording carrier on which printing is to occur) is known from German Patent No. DE 42 21 265 C2. This type of device presupposes a printing head which is freely movable in a direction perpendicular to the recording carrier and includes thickness sensing rollers. An indirectly generated electronic signal (analog signal) emanates from the thickness sensing rollers and is fed to a control unit for the distance setting. In order to produce the signal, a first magnetic element for generating a first magnetic flux is located on the thickness sensing roller. A second magnetic element, generating an opposite second magnetic flux, is located on the printing head carriage. A Hall element is arranged on the printing head carriage in the region of the second magnetic flux, and when a recording carrier is present and the printing head carriage is in a specific lateral position, the drive motor of the distance setting device is activated. The drive motor remains active until the voltage corresponding to an intended or predetermined air gap is applied to the Hall element. This device works relatively accurately, but its accuracy should and can be increased even further. Moreover it is, in part, located in a relatively accessible place on the printing head carriage and is therefore not completely safeguarded from external actions such, for example, as contamination.
Another distance setting device, disclosed in German Patent No. DE 196 11 772 A1, is based on transport rollers which are capable of being resiliently set to the paper thickness and are arranged in pairs on a rigidly mounted driven shaft and on an axis perpendicular to the recording carrier. A measurement signal transmitter arranged on this axis transmits light and cooperates with a measurement signal receiver located on the printing head carriage. Moreover, a position indicator is provided for the printing head carriage. Measurement signals received by the measurement signal receiver are compared with clock pulses of the position indicator, both in the absence of paper and with paper inserted. Based on the resulting difference signal, the printing head distance drive device is operated by a control unit. This type of distance setting device is admittedly cost-effective, because only the measurement signal transmitter and a conventional measurement signal receiver are required. However, it is necessary for the light barrier formed by the light transmitter and light receiver to have highly accurate and stable switch points which cannot be maintained when the ambient and/or operating temperatures for the printer change.
One object on which the invention is based is to eliminate the effect of vibrations caused by stepping motors and the like as they operatively move the carriage supporting the printing head, which often prevent accurate measurement and setting of spacing tolerances between the measuring point and the printing head end face, and thereby to achieve more accurate measurements of the printing substrate thickness and print head position than are attainable in prior art arrangements.
SUMMARY OF THE INVENTION
These and other objects are achieved, in accordance with the invention, in a construction in which the printing head is slightly displaceable (deformable) on the supporting carriage as a result of brief contact with the recording carrier which is supported or carried on the printing abutment. The displacement travel (i.e. distance) and/or a displacement angle of the printing head relative to the recording carrier is measured by means of a reflex sensor located in a clearance defined between the carriage and an opposing printing head housing surface. The result of this measurement, in the form of a processed output signal from an evaluation circuit, controls the drive for automatically setting the spacing of the printing head from the recording carrier or from the printing abutment. During brief contact of the printing head with the recording carrier, a slight “deformation” (which amounts to only a few &mgr;m) of the printing head on and relative to the carriage occurs and is recorded as a signal change by the reflex sensor without any other disturbing influence. This measuring operation can be triggered automatically and is independent of carriage position.
A reliably determined position of the printing head on the carriage is nevertheless obtained, since the printing head is fastened to the carriage by a spring with a front part facing the carriage and with an elastic intermediate layer interposed between the carriage and print head.
The principle of the reflex sensor of the invention may be employed or implemented in many different embodiments. For example, it is contemplated that the reflex sensor be formed from a pairing arranged on the carriage and printing head housing and implemented by a light emitting diode (LED) and a phototransistor located adjacent the LED and both disposed on a surface of the carriage, and a reflex surface disposed opposite the LED and phototransistor on a surface of the printing head housing.
According to another embodiment, the reflex sensor pairing may be formed by a Hall sensor arranged on the carriage and an opposing magnet fastened to the printing head housing.
Furthermore, the desired reflection of waves or beams can also be achieved by forming the reflex sensor pairing as a magnetically sensitive resistor arranged on the carriage in conjunction with an opposing magnet fastened to the printing head housing.
For reflection of optical beams, it is advantageous if the reflex surface of the reflex sensor is implemented by a mirror. Simple polished metal plates are suitable for use as a mirror, and it is unimportant whether reflection is diffuse or specular.
For all electronic or optical elements operating with waves or beams, the presence of external action or external influences on the waves or beams is harmful to the intended functionality. For this reason, in accordance with this invention the pairing, whether implemented by the light emitting diode/phototransistor and associated reflex surface or the Hall sensor and magnet or the magnetically sensitive resistor and magnet, or any other construction, is disposed in a protected space defined, for example, between an enlarged part of the printing head housing and a surface of the carriage that faces away from the printing abutment.
When the printing head is moved toward the recording carrier or the printing abutment, only a very small electric signal is obtained which would be very difficult, if at all, to process. It is therefore desirable that the phototransistor be capable of recording the resulting change in the signal as the printing head is driven into abutment with and contacts the recording carrier.
In accordance with further features of the invention, the signal is modified in that the signal change is fed in the form of a
Dietel Klaus
Eckel Harald
Hauslaib Wolfgang
Stempfle Johann
Cohen & Pontani, Lieberman & Pavane
Tally Computerdrucker GmbH
Yockey David F.
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